The present invention relates to an electric motor bicycle, and more particularly to a unitary self-contained direct drive power module (or "unitary power module") for electric bicycles or other vehicles. The invention also includes a kit for converting a standard bicycle into an electric bicycle by use of the unitary power module.
By way of background information, and turning now to the drawings, FIG. 19(a) illustrates a standard bicycle 100 ("or bicycle"), which is a two wheeled vehicle comprised typically of a front steering wheel 102 and a rear wheel 104, which may be attached to the frame by quick-disconnect units 105. The standard bicycle 100 includes a frame assembly 106 having a head tube 108 which journals a front fork 110 for steering via handle bars 109 by a rider of the bicycle 100. As illustrated in FIG. 19(b), the rear wheel 104 is journalled at the rear end of the frame 106 by a pair of rear stays (or "dropouts") 112. A seat tube 111 is carried by the frame 106 adjacent the rear wheel 104 and a seat post 113 upon which a saddle type seat 115 is positioned thereon to accommodate a rider.
In the standard bicycle 100, a horizontally oriented journal (or crank journal) 117 is positioned beneath the seat tube 111 which supports a rider "propelled" drive mechanism 120. The drive mechanism 120 generally comprises a crank 123 journalled in the crank journal 117, which includes a chain sprocket 129 having a plurality of teeth, together with the crank 123 positioned therein with along with pedals 125 rotatably journalled at each end 127 of the crank 123.
Each wheel typically consists of a tire 114 mounted on a rigid rim 116, an axle 118, a hub mechanism (or "hub") 122 and spokes 124 connecting the rigid rim 116 to the hub 122 to form an axle/hub assembly 121. The hub 122 surrounds the axle 118 and is free to rotate about the axle 118 through a bearing assembly 126 (not shown). The tire/rim assembly 128 is attached to the hub 122 through an assembly of the spokes 124 which are assembled in a woven pattern 130 to form a wheel/hub assembly 140. This woven pattern 130 of spokes has relatively few variations with a large quantity of existing bicycle wheels being common in using the same or similar thirty-six or thirty-four spoke weave pattern 130. A target "chain" sprocket 150 is mounted about the rear wheel 104, and is connected to the crank sprocket 129 by a chain 152 whereby application of power by the rider on the pedals 125 propels the bicycle 100. A derailleur 154 is often substituted for the single target sprocket 150 (or target sprocket), and may have a plurality of sprockets 156, 158, 160, 162, 164 and 166 (illustrated in FIG. 9) to provide variable gearing for rider comfort when either starting or climbing hills or for rider efficiency.
One of the features of a bicycle, is the ability of the wheel to be removed for servicing, such as repairing a flat. As described above, the typical bicycle wheel is constructed of a tire/rim assembly connected to the hub through a series of woven spokes. The hub rides on the axle of the wheel using a bearing assembly. The axle/hub assembly typically has rather loose manufacturing tolerances and as such provides a poor reference frame for the propulsion elements of prior systems. This occurs because bicycles are typically high rate, low-cost, manufactured consumer products, whereby the tolerances of components are not as high as a high quality mechanism. The majority of bicycles sold in the world and in use are in the lower or looser tolerance ranges. Also, when the wheel (or tire) is repaired and then replaced in the dropouts of the frame, the axle can become slightly cocked with respect to the frame. As such, tolerances for the mounting slots of the wheel axle allow for a wide latitude of assembly. The loose manufacturing tolerances of the axle and axle/hub bearings is typical of such low-cost mechanisms. These large tolerances of wheel and bicycle frame components present a significant problem in the design of reliable direct drive propulsion systems where various components of the system are mounted on different parts of the bicycle (e.g., on the frame, on the axle, etc.)
If the various components of the propulsion system are mounted on bicycle components, which have loose tolerances in reference to each other, then the propulsion system suffers (or will suffer) from these same poor alignment tolerances with rough usage. In order to avoid excessive wear, reduced efficiency, and reduced performance as a result of such loose tolerances, an effective propulsion system should ideally utilize a design which is independent of such loose tolerances in the axle/hub assembly of the bicycle as well as the changing tolerances relative to the frame. It is this design concept which forms this invention.
In the past, electric propulsion systems for bicycles have been implemented through a variety of methods which utilized electric motor power to either supplement or replace the above rider drive mechanism in propelling the bicycle. For example, these methods include friction roller drives, belt drives, gear drives, and chain drives. For example, friction drives typically involve the application of an electric motor or "the drive source" to a wheel or "the target mechanism" through a roller mechanism. The roller may be directly attached to the drive source or through a clutch mechanism. The roller transfers the drive source energy through the contact of the roller on the target wheel through friction between their respective surfaces. This type of drive system suffers from mechanical losses associated with slippage between the roller mechanism and the target wheel as a result of reduced friction and from the energy required to compress the rubber tire. Performance in moisture, rain, snow and mud is marginal at best.
By way of further example, electric bicycles having direct drive systems, such as belt, gear and chain drives typically provide higher energy coupling efficiencies than the roller friction drive systems. These systems however require a high degree of mechanical integrity in the geometry of drive components. For instance, there needs to be sufficient tension in the belt and chain of the belt and chain drive systems and the proper alignment or meshing of the gears in the gear drive system. Proper and exact mechanical alignment must be maintained rigidly with shock and many tire and wheel repairs in order to extend the life of the unit.
There have been a number of designs, which can provide direct coupling between an electric motor(s) mounted externally to the rear bicycle wheel and the axle of the wheel. For example, a motor can be mounted either on the diagonal or horizontal rear members (or "stays") of the frame. A direct coupling in these cases can be effected through a 90-degree bevel gear between a shaft from the motor and the axle-hub assembly. In this case, external shocks will cause gear wear. Further, it is difficult to remove the rear wheel for repair. The drive can be effected through a chain, which is better but still mechanically complex and subject to the same kind of problems. It is also difficult to achieve the right reduction ratios between the RPM of typical motors and that of the rear wheel, typically between 10:1 and 25:1. A motor can be mounted above the rear wheel and drive a very large "sprocket" of diameter almost as large as the wheel diameter. Such systems have been demonstrated but have not been accepted because they are clumsy, top-heavy and subject to relative dislocation of the elements.
Other direct drives have been reduced to practice with the motor mounted in the neighborhood of the pedal crank. These can be coupled to the rear wheel by a gear drive with suitable clutches within the crank housing and thence through the usual bicycle chain or through a separate long chain to a separate sprocket on the rear wheel. They can also be coupled to the rear wheel through long shafts and bevel gears. While some of these are workable and practical, they require a special custom bicycle design, which may be more expensive than desired.
For designs in which a motor mounted externally to the rear wheel, an improvement is described in U.S. patent application Ser. No. 08/803,067 entitled "Precision Direct Drive Mechanism for a Power Assist Apparatus for a Bicycle", by Mayer et al. filed on Feb. 20, 1997. In this concept, a motor is mounted on a plate, which is separately indexed to the axle of the rear wheel. The motor drives a pinion gear (or pinion sprocket) which is separately indexed to the axle of the rear wheel, which, through meshed gears, a chain or a belt drives a target gear (or sprocket) which also is attached to the axle through a bearing or free-wheel clutch arrangement. That is, the motor-pinion assembly with its mounting frame and the target gear (or sprocket) are separately indexed off the axle, with the target gear (sprocket) actually indexed from the hub.
Thus, these elements in a benign environment are accurately aligned with respect one another, all being indexed from presumably common and concentric points. However, even with this improved and more compact configuration, we have found in practice that for most bicycles, the axle bearing tolerances and the hub bearing tolerances are highly variable with real world rough usage and shocks. In more detail, if the mesh between the pinion sprocket (or gear) and the target sprocket (or gear) occurs at a long leverage arm from the axle, the looseness of the bearings can change the pinion/target gear meshing or alignment, leading to eventual gear wear, tooth breakage, or misalignments of such sprockets. Additional concerns are the difficulty of achieving the alignment of shafts (such as the shafts of the motor, or the target wheel) and the manufactured tolerances of components over time and with normal rough usage.
Another class of direct drive systems are based on "hub motors" which are designed into the wheel hubs of front or rear wheels. This class of drives has its own cost considerations and performance characteristics.
None of the above described electric bicycle drive propulsion systems provides the important advantages of the inventive unitary power module for an electric bicycle propulsion system which has a high degree of mechanical integrity in the alignment geometry of the drive components even under shock and rough usage. These advantages are achieved by uniquely configuring the unitary power module having drive components comprising a drive source (or an electric motor), a pinion drive coupling component (such as a chain sprocket, gear or pulley pinion or combination thereof), a target mechanism coupling component (or a chain sprocket, driven gear, or belt sprocket), the actual mechanical coupling mechanism to the target or target wheel, and the target or driven wheel, itself, which is the normally the rear wheel. By use of various sprocket ratios, the invention may achieve a wide-range of gear ratios and therefore adaptability to a wide range of motors. Also, by the use of a free-wheel clutch incorporated into the unitary power module, the bicycle is completely free wheeling with virtually no drag in the absence of applied power. Still further, when in production, the unitary power module can be assembled and tested as an integral operating unit, and then be easily and simply attached to the bicycle frame.
Specifically, the present invention achieves these advantages by utilizing a unitary power module having mounting frame assembly on which all propulsion elements are mounted and aligned with a wheel fitting (or "drive") coupler, which is a disk shaped assembly with a large center opening allowing the target coupler to be placed about a wheel axle outside of the hub diameter. In the preferred embodiment, the target coupler has a groove pattern mating the woven spoke pattern of a bicycle wheel to enable the target coupler to be concentrically attached to the target wheel by engagement with the woven spoke pattern by securing elements. The mounting frame is attached to the target coupler by a bearing or the like, including a free wheel clutch. The mounting plate has an opening (or "element") to receive an electric motor to enable a pinion sprocket or gear affixed on the motor to engage the sprocket and through a chain to the target sprocket (or gear) to rotate the target bicycle wheel upon suitable power application by a rider via propulsion controls on the bicycle.
Thus, the present invention provides the advantages of having a separate independent self-contained (and self-aligned) unitary power module which overcomes misalignment problems between the drive source and the target by using a common reference frame. The integrity of the chain alignment or gear mesh is thereby permanently ensured even in rough terrain and rough shock and usage. This invention can thus be advantageously implemented by using a chain drive, gear drive or belt drive system because one of its important advantages is its inherent avoidance of the usual mis-alignment causes by the above prior art devices. It has the additional advantage of being easily installed on almost any bicycle rear wheel by an unique and separately described mechanical coupler. It works efficiently, essentially independent of frame and axle/hub assembly and wheel/hub tolerances.